The present invention relates to an optical head for optically recording and reproducing information on an optical recording medium, and to an optical recording and reproducing apparatus using such optical head. More specifically, the present invention relates to a floating-type optical head that runs over an optical recording medium at a small height above its surface so as to record and reproduce information, and to an optical recording and reproducing apparatus using such floating-type head.
FIG. 19 illustrates a conventional floating-type optical head.
As shown in FIG. 19, the conventional floating-type optical head has a main floating slider portion 120 for forcing the optical head to float at a predetermined height above an optical recording medium 110. This floating slider 120 is provided with a deflection mirror 122 and an objective lens 121. The floating slider 120 is supported by a supporting element 133 wherein the floating slider 120 is pressed toward the optical recording medium 110. The supporting element 133 is fixed to an arm 132 in such a manner that the supporting element 133 may move in radial directions. When the optical recording medium 110 starts rotation, the floating slider 120 goes up and floats there maintaining a certain gap relative to the surface of the optical recording medium 110. A light emitting device 128 such as a laser diode emits a light beam that travels passing through a condensing lens 126, a beam splitter 125, a polarizing plate 124, and a deflecting element 123, and is reflected by a deflection mirror 122. The reflected light beam is then focused onto the optical recording medium 110 by an objective lens 121. The light beam is reflected by the optical recording medium 110 and travels to the beam splitter 125 through the objective lens 121, the deflection mirror 122, the deflecting element 123, and the polarizing plate 124. The light beam is reflected by the beam splitter 125 and then travels passing through a condensing lens 129 and a cylindrical lens 130. Finally, the light beam reaches a photosensor 131, and thus the photosensor 131 detects a signal. The condensing lens 126 is driven by a driving element 127 in directions approximately along its optical axis so that the light beam is focused onto the surface of the optical recording medium 110. A light spot projected onto the optical recording medium is positioned at a correct position on a data track by moving the deflecting element 123 using a fine tracking driver thereby changing an optical path slightly.
However, in the above-described conventional floating-type optical head, only the deflection mirror 122 and the objective lens 121 are installed on the floating slider 120, and optical elements such as the light emitting device 128, the photo-detecting device 131, and the beam splitter 125 are isolated from the floating slider 120.
To achieve easy assembling and adjustment, it is undesirable to reduce the sizes of these optical elements. Therefore, while it is possible to obtain a higher access speed than access speeds of other conventional optical heads, it is impossible to realize an apparatus having a small size comparable to that of a magnetic recording and reproducing apparatus, and thus it is impossible to achieve a high recording density of the apparatus.
In optical heads, there are various kinds of aberrations such as aberrations due to surface irregularities, dimensional inaccuracy, or assembling inaccuracy of optical elements, aberrations of the light emitting device itself, aberrations arising from wavelength variation of a light emitting device due to temperature variation, etc. Unless the aberration is suppressed to a very small level, it is impossible to focus a light beam into a small size of spot. For the above reason, each optical element requires high accuracy. This makes it difficult to achieve lower bit cost.
To improve the recording density of the apparatus, it is also required to solve another problem relating to focus driving means and tracking-mechanism driving means.
In general, a spot of light formed by an optical head has a positioning error arising from dimensional inaccuracy of optical elements or assembling inaccuracy. Furthermore, because an optical recording medium has vibrations in the up-and-down direction during rotation, the focus driving means is required to correctly focus a light beam onto a recording surface.
In a floating-type optical head using a floating slider, the floating slider serves as the focus driving means. However, there is still a positioning error of a spot of light arising from machining inaccuracy or assembling inaccuracy. The floating height of the floating slider varies depending on the linear velocity of a medium or depending on the YAW angle (air inlet angle), and this variation causes a positioning error of the spot of light. For these reasons, a focus driving means is essential for floating-type optical heads. In the above example of the conventional technique, since the deflection mirror 122 and the objective lens 121 are fixed to the floating slider 120, if the floating height of the floating slider varies, the variation between the objective lens 121 and the optical recording medium 110 produces a positioning error of the spot of light.
In the conventional technique, the above problem is avoided by driving the condensing lens 126 in directions along the optical axis using the driving element 127 so that correct focus is maintained.
Furthermore, the data track pitch of an optical recording and reproducing apparatus is generally as small as 1/5 to 1/10 of the data track pitch of a magnetic recording and reproducing apparatus. In most optical recording and reproducing apparatus, a portable optical recording medium or a removable disk is used, and these types of optical recording media used in optical recording and reproducing apparatus have a very large amount of decentering of data tracks compared to the case of magnetic disk storages. A high control gain and a wide control range are required to accomplish high-accuracy and high-speed tracking of a spot of light on a narrow data track. For these reasons, in common optical recording and reproducing apparatus, two-step tracking control with coarse tracking means and fine tracking means is usually employed to perform correct positioning of a spot of light on a data track.
In the above example of the conventional technique, fine tracking control is accomplished by using a fine tracking mechanism to move the deflecting element 123 so as to change the optical path thereby slightly moving the spot of light.
In this technique, however, a deviation occurs between the optical axis of a light beam incident on a lens and the optical axis of the lens, and this aberration limits the minimum size of the spot of light and thus limits the maximum recording density.
As described above, the optical recording and reproducing apparatus needs focus driving means and fine tracking means, and this inevitably causes an increase in the size of the apparatus. As a result, it is difficult to improve the recording density of the apparatus. For these reasons, it is difficult to reduce the size of the optical recording and reproducing apparatus, and therefore, it cannot be installed in a small-size personal computer such as a notebook-size personal computer.